Room-Temperature Weak Ferromagnetism Induced by Point Defects in α-Fe2O3

Unusual room-temperature weak ferromagnetism α-Fe2O3 was prepared by heating the mixture of commercial α-Fe2O3 (as raw material) and tartaric acid at a mild temperature of 250 °C. This reaction involves a fast heating and cooling process resulting from the self-catalyzed oxidation of tartaric acid. Careful chemical analyses confirmed that no any ferromagnetic impurities, such as Fe, Fe3O4, amorphous iron oxide and γ-Fe2O3, were present in the treated sample. The unusual weak ferromagnetism was then attributed to the formation of a large amount of point defects in the treated sample during the peculiar synthetic process. Such a mechanism is supported by the result of annealing, which reduces the amount of point defects and thereby reestablishes the original antiferromagnetism in α-Fe2O3.